1. Field of the Invention
The present invention relates to a heating system for automotive vehicles. Specifically to a system which is capable of transmitting a portion of the heat of the vehicle engine exhaust through a closed-loop heat pipe to a condenser provided downstream of and just behind a heater core.
2. Description of the Prior Disclosure
Recently, there have been proposed and developed various heating systems for automotive vehicles, utilizing exhaust heat from the engine in addition to fluid circulating in the radiator.
One such heating system has been disclosed in Japanese Utility Model First Publication (Jikkai Showa) No. 59-16211. The heating system comprises a main heating system including a heater core connected through a pair of fluid passages to an outlet of a water cooling jacket of the engine and an inlet of a water pump of the engine in such a manner as to be juxtaposed with upper and system including an evaporator section disposed in a manner so as to be in contact with an exhaust passage of the engine and a condenser section disposed downstream of and just behind the heater core. This conventional heating system also includes valve means, such as an electromagnetic valve disposed in the return heat pipe section between the evaporator and the condenser and a discharge air temperature sensor disposed downstream of the condenser, for monitoring the temperature of air flowing through the condenser. In the construction of the conventional heating system, the closed-loop pipe heating system serves as an auxiliary heating system in which sufficiently heated air may be rapidly supplied to the vehicular cabin via the above mentioned arrangement of the pipe heating system, even during engine warm-up when the temperature of radiator coolant is low. In this conventional heating system, if the signal from the air temperature sensor exceeds a predetermined value and sufficient hot water is being supplied from the radiator through the upper radiator hose to the heater core, the above mentioned valve is fully closed and as a result the recirculating flow of working fluid, such as water in the heat pipe is shut off to avoid undesirable over-heating. However, in this conventional heating system, if working fluid remains in the heat pipe section after stopping the engine on winter days or nights in which the ambient temperature is particularly low, there is a possibility that the working fluid will freeze in the heat pipe section. Under such conditions (wherein the working fluid freezes in the heat pipe section) restarting of the closed-loop pipe heating system of the heating system is difficult.
Furthermore, in the conventional heating system, even after the valve provided in the heat pipe closes, a relatively large amount of residual working fluid will remain in the evaporator section to be subsequently evaporated until on residual fluid remains in the evaporator. Thus, this evaporated fluid is supplied as steam to the condenser. Therefore, a further portion of exhaust heat is still transmitted from the evaporator to the condenser after closing the valve. This heat is further transmitter to the vehicular cabin and as a result, the vehicle occupants feel uncomfortable due to momentary over-heating. Additionally, if working fluid trapped in the evaporator section continues to generate steam after the discharge air temperature exceeds the predetermined value and the valve is fully closed, the pressure and temperature of the working fluid in the closed-loop heat pipe may become excessively high, thereby resulting in damage to the closed-loop pipe heating system.